a⋅plomb

/əˈplɒm, əˈplʌm/   [uh-plom, uh-pluhm]  –noun

1. imperturbable self-possession, poise, or assurance.

2. the perpendicular, or vertical, position.

Origin:
1820–30; < F à plomb according to the plummet, i.e., straight up and down, vertical position
Synonyms:
1. composure, equanimity, imperturbability.

Antonyms:
1. confusion, discomposure; doubt, uncertainty.

Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2009.